1. Field of the Invention
The present invention relates to a piping joint structure. In particular, it relates to a piping joint structure that joins adjacent pieces of tubing material by butt welding.
2. Description of Related Art
As a conventional piping joint structure, there is one that is disclosed in a Japanese Unexamined Patent Application, First Publication No. Sho 62-270281. In the piping joint structure disclosed in Japanese Unexamined Patent Application, First Publication No. Sho 62-270281, in the case where stainless steel tubing materials are connected by butt welding, in order to prevent the weld zone from oxidizing on the outer surface side of the tubing materials, a method of inert gas welding from the outer peripheral surface side is used, in which the welding is performed in a state in which air is excluded from the weld zone by an inert gas such as helium gas, argon gas, or the like. Similarly in order to prevent the weld zone from oxidizing on the inner surface side of the tubing materials, so-called back shielding is performed in which the whole pipe is filled with an inert gas such as helium gas, argon gas, or the like.
However, in such a conventional method, a large amount of inert gas is required for back shielding inside the pipe. Therefore, there are problems of uneconomical wastage and high cost.
Furthermore, since it is difficult to completely back shield a pipe whose piping route is complex or long, the weld zone that is located on the inner surface side of the pipe becomes oxidized. Therefore, there is also a problem in that oxidized scale (also called “slag”) occurs.